The correct answer is D. Chlorofluorocarbons.
Greenhouse gases are gases that trap heat in the atmosphere, causing the planet to warm. The main greenhouse gases are water vapor (H2O), carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and ozone (O3).
Chlorofluorocarbons (CFCs) are not greenhouse gases. They are man-made chemicals that were once widely used in refrigerators, air conditioners, and aerosol cans. CFCs are very stable and do not break down in the atmosphere. They can travel up to the stratosphere, where they break down and release chlorine atoms. These chlorine atoms react with ozone molecules, destroying them. Ozone is a layer of gas in the stratosphere that protects the Earth from harmful ultraviolet radiation. The destruction of ozone has led to an increase in the amount of ultraviolet radiation reaching the Earth’s surface, which can cause skin cancer and other health problems.
In 1987, the Montreal Protocol was signed by 197 countries. The Montreal Protocol is an international treaty that phased out the production and use of CFCs. As a result of the Montreal Protocol, the levels of CFCs in the atmosphere have been declining. However, CFCs are still present in the atmosphere and will continue to have an impact on the ozone layer for many years to come.